Diplofuranoxin, a disubstituted dihydrofuranone, was produced together with sphaeropsidin A and epi-sphaeropsidone by Diplodia subglobosa, an emerging ash (Fraxinus excelsior L.) pathogen in Europe

An undescribed disubstituted dihydrofuranone, named diplofuranoxin, was isolated, together with the six well known metabolites sphaeropsidins A and C, epi-sphaeropsidone, mellein and cis- and trans-4-hydroxymelleins, from the fungal species Diplodia subglobosa, an emerging pathogen involved in the ash dieback aetiology in Europe. Currently, the disease represents the main threat to European ash heritage and the wood associated industry. Diplofuranoxin, was characterized essentially by NMR and HRESIMS spectra as (3Z)-3-(2,3-dihydroxybutylidene)-5-methyldihydrofuran-2(3H)-one. Its relative and absolute configuration was determined by joining NOESY NMR experiments and computational analysis of electronic circular dichroism spectrum. All the metabolites were screened for phytotoxic, antioomycetes and zootoxic activities and only sphaeropsidin A and epi-sphaeropsidone were active in two out of three bioassays performed. In addition, sphaeropsidin A completely inhibited mycelium growth of Phytophthora cambivora, whereas the inhibition rate of epi-sphaeropsidone was less than 50% at the higher concentration used. Both metabolites were inactive in the Artemia salina assay. Results obtained in this study have allowed to characterize for the first time the main metabolites produced in vitro by D. subglobosa and to increase the knowledge on the metabolic profile of Botryosphaeriaceae for a correct taxonomic classification of the strains belonging to this family.